Self-cleaning metering device

ABSTRACT

In a fluid metering device for metering a fluid from a supply source to means of use of this fluid comprising a metering valve able to slide in a sleeve over a travel C, this valve comprising an intake orifice ( 16 ) for admitting the fluid from the said supply source and an orifice ( 18 ) for ejecting this fluid to the means of use, there are provided means ( 20 ) for channelling the fluid intended to allow, during the movement of the metering valve in its sleeve, a sweeping of the fluid over all the contacting surfaces of the valve and of the sleeve. The means of channelling the fluid advantageously comprise a helical groove of width L and of pitch P.

FIELD OF THE INVENTION

[0001] The present invention relates to the general field of devices forcontrolling fluid flowrate and it is more particularly concerned with aself-cleaning metering device.

PRIOR ART

[0002] It is known that in valves used for regulation, the operationalguidance lengths give rise to friction which then generates a hysteresisphenomenon. This friction is all the greater since the contaminationwhich exists in any fluid causes the creation of “gums” on thecontacting guiding surfaces.

[0003] In the particular case of the metering devices of fuel injectionsystems, in turbojets or turboprops (more generally referred to asturbomachines), this hysteresis causes a heterogeneity of the injectionflowrate which could impair the proper operation of the turbomachine,especially at the time of switch-on thereof.

[0004] A solution to this problem conventionally consists in reducingthe frictional surface areas. However, this solution has the majordrawback of increasing the contact wear of the remaining operationalsurfaces and therefore of limiting the lifetime of the metering device.Another solution consists in reducing the coefficient of friction of thecontacting surfaces. However, here again, this solution proves to beinadequate when the build-up of gums or/and of contaminants becomes toolarge.

OBJECT AND DEFINITION OF THE INVENTION

[0005] It is therefore an object of the present invention to alleviatethese drawbacks by proposing a fluid metering device which makes itpossible to appreciably reduce or even to eliminate any build-up ofcontaminants due to the movement of the fluid through the device.

[0006] These aims are achieved by a fluid metering device for metering afluid from a supply source to means of use of this fluid comprising ametering valve able to slide in a sleeve over a travel C, the said valvecomprising an intake orifice for admitting the fluid from the saidsupply source and an orifice for ejecting this fluid to the said meansof use, characterized in that it comprises means of channelling thefluid intended to allow, during the movement of the metering valve inits sleeve, a sweeping of the fluid over all the contacting surfaces ofthe said valve and of the said sleeve.

[0007] With this particular structure, the fluid is compelled to sweepall the contacting surfaces. Self-cleaning of the device is thusensured, thereby preventing the build-up of contaminants, and thecreation of “gums”, by discharging them with the metered fluid.

[0008] Advantageously, the means of channelling the fluid comprise ahelical groove of width L and of pitch P.

[0009] According to the embodiment envisaged, the means of channellingthe fluid may be disposed on the said metering valve or on the saidsleeve.

[0010] Preferably, the travel C of the metering valve is greater than orequal to the distance P-L.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The characteristics and advantages of the present invention willbecome more apparent from the following description, given by way ofnon-limiting indication, in conjunction with the appended drawings inwhich:

[0012]FIG. 1 is a perspective view illustrating a metering deviceaccording to the invention, and

[0013]FIGS. 2 and 3 are two sectional views of the metering device ofFIG. 1 in two positions characteristic of its mode of operation.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0014]FIG. 1 illustrates in perspective a metering device in accordancewith the invention, intended for supplying means of use (notrepresented) with a pressurized fluid fed from a supply source (notrepresented). An exemplary application of such a metering device isgiven with a system for injecting fuel into a combustion chamber of aturbomachine.

[0015] Under the action of the fluid subjected to a specified supplypressure, a metering valve 10 can slide in a cylindrical sleeve 12between an initial closure position in which the valve blocks the fluidand comes into contact against a seal 14 disposed level with a fluidintake orifice 16 (see FIG. 2) , and a terminal opening position inwhich the fluid can pass through the metering device and flow towardsthe means of use of this fluid through an ejection orifice 18 in theform of slots made in the metering valve and whose flow cross sectionsare dimensioned so as to ensure the desired metered dose at the level ofthese means of use (see FIG. 3).

[0016] According to the invention, the metering valve comprises means 20for channelling the fluid intended to allow, during the movement of themetering valve in its sleeve, over its entire travel C, a sweeping ofthis fluid over all the contacting surfaces of the valve and of thesleeve. These channelling means are, preferably, constituted by ahelical groove of width L whose pitch P is specified in such a way that,during each valve opening/closing cycle, the fluid sweeps all thecontacting surfaces and thus removes the contaminants which may havebuilt up there.

[0017] Thus, if one considers the travel C of the valve and the pitch Pof the groove whose width L is, in the example illustrated, equal toP/2, this condition will be realized if C is greater than or equal toP/2. More generally (for cases where the ratio of the pitch of thegroove to its width is not equal to ½), this condition will be satisfiedif the travel C of the valve is greater than or equal to the distanceP-L (difference between the pitch P and the width L).

[0018] Of course, the magnitude of the depth of the groove will becalculated to accommodate the desired fluid flowrate and avoid overlylarge head losses in the means of use.

[0019] It will be noted that whereas, in the example illustrated, thegroove 20 is made in the valve 10, it is quite obvious that it is alsoentirely conceivable to form it in the sleeve 12. In one or other ofthese two alternative configurations, the groove, by also ensuring ascraping of the contacting surfaces, makes it possible to detach thecontaminants built up on them. Furthermore, the sweeping effected by thefluid at the level of these channelling means constituted by the helicalgroove 20 allows discharge of these contaminants to the means of use ofthe fluid and thus achieves self-cleaning of the metering valve.

1. Fluid metering device for metering a fluid from a supply source tomeans of use of this fluid comprising a metering valve (10) able toslide in a sleeve (12) over a travel C, the said valve comprising anintake orifice (16) for admitting the fluid from the said supply sourceand an orifice (18) for ejecting this fluid to the said means of use,characterized in that it comprises means (20) of channelling the fluidintended to allow, during the movement of the metering valve in itssleeve, a sweeping of the fluid over all the contacting surfaces of thesaid valve and of the said sleeve.
 2. Fluid metering device according toclaim 1, characterized in that the said means of channelling the fluidcomprise a helical groove of width L and of pitch P.
 3. Fluid meteringdevice according to claim 1 or claim 2, characterized in that the meansof channelling the fluid are disposed on the said metering valve. 4.Fluid metering device according to claim 1 or claim 2, characterized inthat the means of channelling the fluid are disposed on the said sleeve.5. Fluid metering device according to claim 2, characterized in that thetravel C of the metering valve is greater than or equal to the distanceP-L.
 6. Fuel injector for a turbomachine combustion chamber comprising afuel metering device according to any one of claims 1 to 5.